Thermal Shock Behaviour of Open-Cell Cordierite Foams

Abstract:

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Open-cell ceramic foams are being considered for a variety of applications owing to their high permeability and low weight, including molten metal filters, catalytic substrates and radiant burners. In these applications, foams are exposed to high temperatures and thermal gradients and thus the materials used require resistance to severe thermal stresses during service. Unfortunately, little is known about the thermal shock behaviour of cordierite foams when subjected to sudden
changes in temperature. The objective of the present study was to investigate the thermal shock behaviour of two kinds of cordierite-based ceramic foams manufactured by the replication process. Thermal shock experiments were carried out by rapidly transferring the heated samples from a resistance furnace to
a quenching bath containing distilled water followed by measuring of the retained flexural strength. Unlike dense cordierite samples that showed a sudden decrease in flexural strength at quench temperature differences above 325 K, the strength retained after thermal shock by open-cell cordierite foams decreased gradually with increasing quench temperatures. This suggests a cumulative damage mechanism reflecting an increase in damage throughout the material rather than sudden failure owing to propagation of pre-existing cracks.

Abstract: Molten Soda lime glass (SLG) was penetrated into the surface of ZTA at 1500°C for the
holding time of 1 to 10 h. The depth of the glass penetration increased with increasing holding time.
The thermal expansion mismatch and elastic property mismatch between the penetrated glass and
ZTA produced residual compression in the surface region during cooling. This residual compression
enhanced the flexural strength and fracture toughness remarkably.

Abstract: The heating style of the plane mould has great influence on the mechanical properties of E-SMC parts. In this paper, the temperature distribution of the plane mould (general heating style and thermal optimized heating style) and the mechanical properties and the cross section morphology of E-SMC samples were systematically studied. The results showed that there existed 30°C difference between the highest temperature point and the lowest temperature point in the general heating mould cavity, the difference of flexural strength between the samples cut from the centre and those cut from the corner was about 140MPa, otherwise, the fiber distribution of the fracture cross section was extremely uneven and the fibers were poorly adhered with epoxy resin. While, in the thermal optimized mould cavity, the surface temperature was much more even and the difference between the highest temperature point and the lowest temperature point was less than 10°C. And the flexural strength between the samples cut from the centre and those cut from the corner was close to be 320MPa. The fiber distribution of the fracture cross section was even and the fibers were well adhered with epoxy resin.

Abstract: High-temperature mechanical properties, machinability, oxidation resistance and thermal shock resistance of different content of carbon particles modified silicon carbide composite ceramics (Cp/SiC) prepared by pressureless sintering techniques were studied. Adhesion of Cp/SiC to melted glass under 1000°C was also observed. The results showed that 15-Cp/SiC had the optimum machinability and it also did not adhere to melted glass at high temperature. And flexural strength, hardness, and fracture toughness of 15-Cp/SiC is 136.5MPa, 274.6kgf/mm2, 2.58MPa•m1/2 respectively. The good performance of Cp/SiC made it possible to be used as high temperature glass fixture, which means that Cp/SiC can not only improve the service life of fixture materials, but also broaden the application fields of SiC ceramics.

Abstract: Silicon nitride nanoceramics were fabricated by hot press sintering two kinds of Si3N4 nano-sized powders. The effect of starting powders on microstructure, mechanical properties and thermal shock resistance were investigated. The microstructure of sintered materials consists of spherical grains and the addition of α–Si3N4 to starting powders does not affect the grain morphology. The flexural strength, fracture toughness and thermal shock resistance increase with the increase in amount of α–Si3N4 starting powders, and the maximum mechanical properties are obtained when the amount of α–Si3N4 powders is 40wt.%. The hardness values decrease with the increase of α–Si3N4 amount.